Ejector vapor recovery system for stored volatile liquids

ABSTRACT

A process of separating a volatile liquid vapor from admixture with air by pressurizing a liquid stream which is at a temperature below its boiling point, feeding the pressurized liquid stream through an ejector to a lower pressure, conducting a stream of air and vapors of the liquid to the suction side of the ejector to form an admixture of liquid, liquid vapor and air, at a pressure intermediate the pressure of the streams fed to the ejector but adequate to condense the volatile liquid vapors to liquid, and gravity separating the volatile liquid, including condensed vapor, from the air.

United States Patent Sudduth Dec. 18, 1973 EJECTOR VAPOR RECOVERY SYSTEM3,613,333 10/1971 Gandenier 55/89 3,284,992 11/1966 Wickman 55/7I FORSTORED VOLATILE LIQUIDS [75] Inventor: Jackie Wayne Sudduth, Brookfield,

Ill

[73] Assignee: Chicago Bridge & Iron Company, Oak Brook, Ill.

[22] Filed: Apr. 12, 1972 [21] Appl. No.: 243,187

52 us. ca. 55/55, 55/84 [5i] Int. Cl B0ld 19/00 [58] Field of Search55/52, 55, 88, 89; 62/54 [56] References Cited UNITED STATES PATENTS2,947,379 8/1960 Aubrey 55/88 Primary Examiner-Charles N. HartAttorney-Charles J. Merriam et al.

[57] ABSTRACT A process of separating a volatile liquid vapor fromadmixture with air by pressurizing a liquid stream which is at atemperature below its boiling point, feeding the pressurized liquidstream through an ejector to a lower pressure, conducting a stream ofair and vapors of the liquid to the suction side of the ejector to forman admixture of liquid, liquid vapor and air, at a pressure intermediatethe pressure of the streams fed to the ejector but adequate to condensethe volatile liquid vapors to liquid, and gravity separating thevolatile liquid, including condensed vapor, from the air.

8 Claims, 1 Drawing Figure EJECTOR VAPOR RECOVERY SYSTEM FOR STOREDVOLATHLE LIQUIDS This invention relates to apparatus and processes forstoring volatile liquids. More particularly, this invention is concernedwith methods and apparatus for recovering vapors of volatile liquidsfrom mixtures with air.

Many volatile liquids, including gasoline, kerosene, fuel oil, crude oiland benzene, are widely used industrially and commercially. These andother volatile liquids are routinely transported various distances bypipeline, railroad tank car, tank truck, ship or barge. Upon arrival ata destination, the volatile liquid is normally stored in a storage tankpending use or further distribution.

Because the boiling point of many of the liquids is generally quitehigh, such as 150 F or higher, the liquid can be readily stored at aboutatmospheric pressure or slightly above and the use of tanks designed towithstand greater pressures avoided. The tanks used are generally thinmetal shells capable of withstanding the hydrostatic load and only arelatively small variation, internally and externally, from atmosphericpressure. Therefore, it is conventional when a product is removed fromsuch a tank to permit air to flow in to equalize internal and externalpressures. Similarly, when a tank is being filled with liquid, means areprovided to vent or remove vapor and air so the internal pressure doesnot exceed safe pressure levels.

Venting the mixture of vapor and air to the atmosphere is undesirablebecause of the resulting air pollution and loss of valuable vapors.Although vapors can be condensed from the mixture by refrigeration andthe air, virtually free of vapors, then vented to the atmosphere, thecapital investment in a refrigeration system, and necessary start uptime, deters this approach. There is accordingly a need for analternative process and apparatus which can be used to separate orrecover vapor from admixture with air.

According to the present invention, there is provided, the process ofseparating a volatile liquid vapor from admixture with air whichcomprises pressurizing a volatile liquid stream which is at atemperature below its boiling point, feeding the pressurized volatileliquid stream to the inlet side of an ejector and through an ejectoroutlet to a lower pressure thereby creating a suction side in theejector, conducting a stream of air and vapors of the volatile liquid tothe suction side of the ejector to form an admixture of volatile liquid,volatile liquid vapor and air, at a pressure intermediate the pressureof the streams fed to the ejector but adequate to condense the vapors toliquid, and gravity separating the volatile liquid, including condensedvapor, from the air. The liquid leaves the ejector at a lower pressurethan at which it was fed to it but, since the temperature of the liquidis comparatively the same or little different, the pressure is adequateto keep it liquid. The process is particularly useful when the streamsare at about ambient temperature and/or when the mixture of vapors andair is at about atmospheric pressure or slightly thereabove.

Separation of the volatile liquid, including the condensed vapor, fromthe air can be readily achieved in any suitable way. In one method themixture which leaves the ejector can be conducted to a separator vessel.The liquid can be separated in the vessel, such as by gravity, andthereafter the liquid can be removed and returned to a storage tankwhile the air, low in vapor, can be vented to the atmosphere.

An advantage of the process is that a liquid pump can be used topressurize the volatile liquid fed to the ejector. Use of a moreexpensive vapor compressor is thereby avoided. In addition, since thevapor-air mixture can be explosive the high spark risk associated withuse of a compressor, if permitted at all, to pressurize the mixture isavoided. Furthermore, more of the conduits can be liquid pipes, whichare less expensive and smaller, rather than vapor pipes.

Also provided by the invention is a novel combination of apparatus forrecovering the vapor of a volatile liquid from admixture with air. Theapparatus comprises a storage tank, a liquid conduit from the storagetank to a liquid pump, a liquid conduit from the liquid pump to theinlet side of an ejector, a vapor conduit from the vapor space of thestorage tank to the suction side of the ejector, a conduit from theoutlet side of the ejector to a gravity separator vessel, a conduit fromthe separator vessel to a disposal means for venting air from theseparator vessel, and a liquid conduit from the separator vessel to thestorage tank for returning volatile liquid. Also included is suchancillary apparatus as would normally be included in a storage systemfor a volatile liquid.

The invention will be described further in conjunction with the attacheddrawing which shows schematically a novel combination of apparatususeful in practicing the process of this invention.

Storage tank 10, as shown in the drawing, is a conventional storagetank. Conduit 14 feeds a volatile liquid through valve 15 and conduit 16to fill the tank. Valve 15 is closed when filling stops. When liquid isto be removed from tank 10 for distribution or shipment it is removedthrough conduits 16 and 14 with valve 15 open.

In order to maintain a suitable pressure inside of tank 10 duringemptying operations, conduit 17 is provided at the top of the tank incommunication with vapor space 20. Conduit 17 is connected to valve 18which is connected in turn to conduit 19. Valve 18 is opened to permitair to flow through conduits l9 and 17 into the tank during removal ofvolatile liquid from the tank.

During filling of tank 10 with a volatile liquid, the vapor space isreduced and vapor must be removed to prevent over pressurizing the tank.The vapor is removed from the tank by vapor conduit 22 whichcommunicates with the tank vapor space and the suction side of ejector23.

A stream of volatile liquid 21 is removed from tank 10 by liquid conduit24 which communicates with the lower part of the tank and liquid pump25. The pressure of the volatile liquid is increased by pump 25 to apressure substantially higher than in tank 10, and advisably to apressure of about 400 to 550 psia. The pressurized volatile liquidstream is fed by conduit 26 from pump 25 to the inlet side of ejector23. The pressurized volatile liquid flows through the ejector andthereby produces suction or a reduced pressure in communication withvapor conduit 22 thereby causing a stream of vapor to be pushed into thesuction side of the ejector.

The stream from the outlet of ejector 23 is fed by conduit 27 toseparator vessel 28. The stream constitutes an admixture of volatileliquid, volatile liquid vapor and air. The admixture is at a pressurebetween the pressure in vapor space 20 and the pressure of the volatileliquid stream fed by conduit 26 to the ejector. lt is essential in anyevent that the pressure of the admixture be sufficiently high to causecondensation of the volatile liquid vapor at the temperature of thestream.

When the admixture stream reached separator vessel 28 by conduit 27, thevolatile liquid, including condensed volatile liquid vapor, separatesfrom the air by gravity. Air, including some uncondensed vapor, is fedfrom vessel 28 by conduit 29 through valve 33 and conduit 34 fordisposal in a suitable manner. Because the amount of vapor in the air issmall, it can be vented to the atmosphere or flared.

Volatile liquid is removed from vessel 28 by conduit 30 which feeds itthrough valve 31 to conduit 32 which conveys the liquid back to tank 10.

In operating the process and apparatus of the invention, the pressure ofthe mixture in conduit 27 is below the pressure in conduit 26 andsubstantially above the air-vapor mixture pressure in conduit 22. It isadvisable to create a pressure in conduit 27 as high as reasonablypractical so that the amount of vapor condensed and removed leaves theair very low in vapor and desirably containing not more than volumepercent vapor. Since the volume percent of vapor in the gaseous mixturein vessel 28 is determined by the formula:

Vol. percent 100 X vapor pressure of volatile liquid/total pressure itcan be readily seen that the vapor remaining in the air is reduced withincrease in total pressure. The energy from the pump eventually ends upas heat in the contents of the tank but itis dissipated by heat transferthrough the uninsulated tank to the ambient air.

The invention is considered particularly useful in recovering vapors ofstored organic liquid materials which have a boiling point of about 150to 350 F.

J The following example is presented to further illustrate theinvention.

Example Crude oil having a vapor pressure of 8 psia at 80 F is filledinto tank 10 of the drawing. The vapor space 20 has a pressure of psiaand is at 80 F.

Crude oil at 80 F is removed from tank 10 by conduit 24, pressurized bypump 25 and sent at 500 psia at a flow rate of 212,000 lbs/hr to ejector23. Vapor and air are removed at 80 F from tank 10 by conduit 22 and fedat 15 psia and a flow rate of 4,020 lbs/hr to the suction side ofejector 23.

The admixture at 80 F and l 15 psia flows from the outlet of ejector 23at a rate of 2 l 6,020 lbs/hr to vessel 28 where the liquid separates bygravity from the air. The air, containing less than 7 volume percentcrude oil vapor, at 80 F and l 15 psia is vented by conduit 29 to theatmosphere at a rate of 3,740 lbs/hr. Liquid crude oil at 80 F and 1 l5psia is fed from vessel 28 at a rate of 213,861 lbs/hr to conduit 30which conveys it through open valve 31 to conduit 32 and then to tank10.

The foregoing detailed description has been given for clearness ofunderstanding only, and no unecessary limitations should be understoodtherefrom, as modifications will be obvious to those skilled in the art.

What is claimed is:

1. The process of separating a volatile liquid from admixture with airwhich comprises:

pressurizing a volatile liquid stream which is at a temperature belowits boiling point,

feeding the pressurized volatile liquid stream to the inlet side of anejector and through an ejector outlet to a lower pressure therebycreating a suction side in the ejector,

conducting a stream of air and vapors of the volatile liquid to thesuction side of the ejector to form an admixture of volatile liquid,volatile liquid vapor and air, at a pressure intermediate the pressureof the streams fed to the ejector but adequate to condense the vapor toliquid, and

separating the volatile liquid, including condensed vapor, from the air.

2. The process of claim 1 in which the streams are at about ambienttemperature.

3. The process of claim 1 in which the mixture of vapors and air is atabout atmospheric pressure or slightly thereabove.

4. The process of claim 1 in which pressurizing of the volatile liquidstream is effected by a liquid pump.

5. The process of claim I in which the admixture is conveyed from theejector to a separator vessel and the liquid separated from air therein.

6. The process of claim 1 in which the liquid is an organic liquidmaterial having a boiling point of about to 350 F.

7. The process of separating a volatile liquid vapor from admixture withair which comprises:

removing a volatile liquid stream at a temperature below its boilingpoint from a storage tank containing such liquid and a mixture of airand vapor from the liquid,

pressurizing the volatile liquid stream,

feeding the pressurized volatile liquid stream to the inlet side of anejector and through an ejector outlet to a lower pressure therebycreating a suction side in the ejector,

conducting a stream of air and vapors of the volatile liquid from thetank to the suction side of the ejector to form an admixture of volatileliquid, volatile liquid vapor and air, at a pressure intermediate thepressure of the streams fed to the ejector but adequate to condense thevapors to liquid, and

separating the volatile liquid, including condensed vapor, from the air.

8. Apparatus comprising:

a storage tank for a volatile liquid,

a liquid conduit from the storage tank to a liquid a liquid conduit fromthe liquid pump to the inlet side of an ejector,

a vapor conduit from the vapor space of the storage tank to the suctionside of the ejector,

a conduit from the outlet side of the ejector to a gravity separatorvessel,

a conduit from the separator vessel to a disposal means for venting airfrom the separator vessel, and

a liquid conduit from the separator vessel to the storage tank forreturning liquid thereto.

vapor

2. The process of claim 1 in which the streams are at about ambienttemperature.
 3. The process of claim 1 in which the mixture of vaporsand air is at about atmospheric pressure or slightly thereabove.
 4. Theprocess of claim 1 in which pressurizing of the volatile liquid streamis effected by a liquid pump.
 5. The process of claim 1 in which theadmixture is conveyed from the ejector to a separator vessel and theliquid separated from air therein.
 6. The process of claim 1 in whichthe liquid is an organic liquid material having a boiling point of about150* to 350* F.
 7. The process of separating a volatile liquid vaporfrom admixture with air which comprises: removing a volatile liquidstream at a temperature below its boiling point from a storage tankcontaining such liquid and a mixture of air and vapor from the liquid,pressurizing the volatile liquid stream, feeding the pressurizedvolatile liquid stream to the inlet side of an ejector and through anejector outlet to a lower pressure thereby creating a suction side inthe ejector, conducting a stream of air and vapors of the volatileliquid from the tank to the suction side of the ejector to form anadmixture of volatile liquid, volatile liquid vapor and air, at apressure intermediate the pressure of the streams fed to the ejector butadequate to condense the vapors to liquid, and separating the volatileliquid, including condensed vapor, from the air.
 8. Apparatuscomprising: a storage tank for a volatile liquid, a liquid conduit fromthe storage tank to a liquid pump, a liquid conduit from the liquid pumpto the inlet side of an ejector, a vapor conduit from the vapor space ofthe storage tank to the suction side of the ejector, a conduit from theoutlet side of the ejector to a gravity separator vessel, a conduit fromthe separator vessel to a disposal means for venting air from theseparator vessel, and a liquid conduit from the separator vessel to thestorage tank for returning liquid thereto.